The present invention relates to an angle adjuster for a music stand and a keyboard instrument with the angle adjuster.
In manufacturing of keyboard instruments, it has today become a big issue in product development how many functions can be provided in a keyboard instrument while reducing manufacturing costs.
In a conventional keyboard instrument 100, including a structure to raise a music stand 190 laid down on a top plate 192 toward a player side and to set up the music stand 190 on the top plate 192 as shown in FIG. 4, there is used a special hinge 199 having two joints as shown in FIG. 5A (see, for example, Trade Name: CA93, page 45 of Kawai General Catalogue of Educational Musical Instruments and Devices (issued March, 2012)).
The hinge 199 includes a first portion 199a configured to be attached to the top plate 192, a second portion 199b pivotably attached to the first portion 199a and configured to be attached to the music stand 190, and a third portion 199c pivotably attached to the second portion 199b. 
The first portion 199a is provided, at a free end thereof, with a projection 199d to catch a free end of the third portion 199c. 
Also, in the hinge 199, the second portion 199b is configured to have a length such that, when the music stand 190 is folded, a joint 199e between the second portion 199b and the third portion 199c is located on an inner side of the projection 199d of the first portion 199a, as shown in FIG. 6. This is because if the joint 199e is located on an outer side of the projection 199d of the first portion 199a when the music stand 190 is folded, the joint 199e may hit and damage the top plate 192.
In a case of raising the music stand 190 toward the player side and setting up the music stand 190 on the top plate 192 by means of the hinge 199, the free end of the third portion 199c is made to be caught by the projection 199d provided at the free end of the first portion 199a, so that the first portion 199a, the second portion 199b, and the third portion 199c are secured in a triangular arrangement as shown in FIG. 5B.